Creating Functional Nanocrystal-Molecule Interfaces for Spin-triplet Energy Transfer

化学学部的大分子、超分子和纳米化学项目支持德克萨斯大学奥斯汀分校的Sean T. Roberts教授研究发生在材料中的光触发过程。光通过光合作用为植物生长提供能量，用于无线通信的电子设备，甚至形成了非侵入性医学治疗的基础，例如用于治疗癌症的光动力疗法。然而，光通过被称为光子的粒子以一种特殊的方式传递能量。不同颜色的光含有不同能量的光子，光子能量与其预期应用相匹配是很重要的。能量过少的光子无法完成预期的任务，而能量过多的光子浪费能量，并可能导致组件损坏。该研究项目开发的材料可以通过将光子对组合成单个高能光子或将单个光子转换成多个低能光子来重塑光的能量含量。一旦形成，这些材料可以作为能量转移剂，改善太阳能收集和量子计算。除了在研究项目上与学生密切合作外，罗伯茨教授还创立并参与了德克萨斯绿色能源项目（GREAT），该项目由德克萨斯大学奥斯汀分校和奥斯汀社区学院共同成立。GREAT旨在增加通过有针对性的指导和研究经历获得学位的社区大学生的数量。与有机染料分子化学功能化的半导体量子点为光子转换提供了理想的界面。被光吸收激发的量子点可以将它们的能量传递给表面的分子，促进它们进入自旋三态激子状态。如果大量形成，成对的自旋三重态激子可以经历三重态聚变，这一过程将它们的能量结合在一起，形成一个可以辐射光的高能量自旋单线态。同样地，光激发染料分子可以推动三重态聚变的逆向过程，单线态裂变，产生成对的三重态激子，每个激子都可以通过量子点来驱动红外光发射。这些方案需要一个关键步骤，即自旋-三重态激子在量子点分子界面上的转移，然而这些界面的结构如何影响自旋-三重态激子转移的速率和效率的理解是难以捉摸的。为了满足这一需求，德克萨斯大学奥斯汀分校的罗伯茨教授领导了一个采用受控化学合成、二维核磁共振和飞秒时间分辨光谱以及电子结构计算的团队。研究小组研究了量子点的化学结构：由PbS和Si两种互补量子点材料形成的分子界面如何影响自旋三重态激子转移。该项目有助于创造新的混合有机：无机结，用于光驱动能源和燃料的生产，以及使用自旋纠缠进行量子计算和信息存储的材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division supports Professor Sean T. Roberts at the University of Texas at Austin to study light-triggered processes that occur in materials. Light provides the energy that fuels plant growth via photosynthesis, is used in electronics for wireless communication, and even forms the basis for noninvasive medical treatments, such as photodynamic therapy used to treat cancer. However, light transmits its energy in a peculiar manner, via particles known as photons. Different colors of light contain photons with different amounts of energy, and it is important that photon energies be matched to their intended applications. Photons with too little energy are unable to meet their intended task while photons with too much energy waste energy and can cause damage to components. This research project develops materials that reshape light’s energy content by combining pairs of photons into a single high-energy one or converting individual photons into multiple lower-energy photons. Once formed, these materials can serve as energy transfer agents improving solar energy harvesting and quantum computation. In addition to working with students closely on the research projects, Professor Roberts also founded and participates in the GReen Energy At Texas (GREAT) program, which was formed between the University of Texas at Austin and Austin Community College. GREAT aims to increase the number of community college student that earn degrees through targeted mentorship and research experiences.Semiconductor quantum dots chemically functionalized with organic dye molecules offer an ideal interface for photon conversion. Quantum dots energized by light absorption can pass their energy to molecules at their surface, promoting them into spin-triplet exciton states. If formed in high quantity, pairs of spin-triplet excitons can undergo triplet fusion, a process that combines their energy to form a single high-energy spin-singlet state that can radiate light. Likewise, photoexciting the dye molecules can fuel triplet fusion’s inverse process, singlet fission, which creates pairs of triplet excitons that can each pass to the quantum dot to drive infrared light emission. These schemes require a key step, the transfer of a spin-triplet exciton across the quantum dot:molecule interface, yet an understanding of how the structure of these interfaces impacts the rate and efficiency of spin-triplet exciton transfer is elusive. To address this need, Professor Roberts at the University of Texas at Austin directs a team that employs controlled chemical synthesis, 2D NMR and femtosecond time-resolved spectroscopies, and electronic structure calculations. The research team investigates how the chemical structure of quantum dot:molecule interfaces formed by two complementary quantum dot materials of PbS and Si impact spin-triplet exciton transfer. This project contributes to the creation of new hybrid organic:inorganic junctions for light-driven production of energy and fuels as well as materials that use spin entanglement for quantum computation and information storage.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.